1. Field of the Invention
The invention relates to a pilot-operated flow regulating valve including a main valve element arranged in a flow passage to which high-pressure fluid is supplied, a circular valve seat formed in said flow passage, said main valve element facing said valve seat, a pressure receiving member arranged with its front surface exposed to the fluid in said flow passage, said pressure receiving member being moveable in accordance with a differential pressure between a fluid pressure applied to said front surface in a first portion of said flow passage and a pressure in a pressure control chamber bounded by a rear surface of said pressure receiving member, a driving force transmitting member interposed between said pressure receiving member and said main valve element so as to move said pressure receiving member and said main valve element in directions such that said main valve element moves towards said valve seat into a first, completely seated position and away from said valve seat into other positions allowing a fluid flow through said valve seat, a pilot passage connecting said pressure control chamber with said second portion of said flow passage located at a side of said valve seat opposite to said pressure receiving member, a leak passage of small cross-sectional area permitting leak of fluid between said pressure control chamber and said first portion of said flow passage, urging means for urging said main valve element in a direction opposite to a driving direction of said pressure receiving member, and a pilot passage constant differential-pressure regulating valve which opens when a differential pressure between an inlet and an outlet of said pilot passage becomes higher than a given pressure in order to keep said differential pressure essentially constant In operation of said pilot-operated flow regulating valve the differential pressure between the inlet and the outlet sides of the valve is kept constant to thereby regulate the flow rate of fluid through said valve seat.
2. Discussion of the Related Art
In flow regulating valves in general the differential pressure between the inlet and outlet sides of the valve is regulated by a solenoid such that the flow rate is controlled in accordance with the set differential pressure. For extremely high fluid pressures, however, the solenoid needs to be strong and has to have a huge size when directly actuating the main valve element, compared with the cross-sectional area of the flow passage for the fluid. Strong solenoids are expensive. Said combination lacks practicability.
To avoid said drawback it is known in practice to use pilot-operated types of flow regulating valves for a high pressure applications. Unlike a simple pilot-operated on/off valve, pilot-operated flow regulating flow valves need a constant differential-pressure regulating pilot valve for opening and closing a pilot passage. The solenoid then only needs to be strong enough to actuate the pilot valve which is actuatable by much less force than the main valve element. As a result, a small sized, cheap solenoid, preferably a proportional solenoid, can be used, the actuating force of which is proportional to the value of the current supplied to its coil.
In a conventional pilot operated flow regulating valve the main valve element is arranged in a flow passage for high-pressure fluid and faces the valve seat formed in the flow passage. At the rear side of a pressure receiving member a pressure control chamber is defined. The front surface of the pressure receiving member is exposed to the fluid in the first portion of said flow passage so that the pressure receiving member moves in response to different pressures applied to its front and rear surfaces. A driving force transmitting member is interposed between said pressure receiving member and the main valve element. Also, a pilot passage connects said pressure control chamber with a second portion of the flow passage located below said valve seat opposite the pressure receiving member front surface. A leak passage of small cross-sectional area permits leak of fluid between the pressure control chamber and said first portion of the flow passage. Urging means urge the main valve element in a direction opposite to the driving direction of said pressure receiving member. Said design of a pilot operated flow regulating valve is known from practice. In said conventional pilot-operated flow regulating valve said main valve element when lifted from its valve seat is in a state that it can freely vibrate, e.g. in lateral direction. If said main valve element occasionally vibrates because of the fluid flow and repeatedly collides with its surrounding, e.g. the valve seat, disturbing noise is produced. Said phenomenon is known as "valve rattling". Furthermore, excessive wear may develop at the main valve element and/or at the valve seat.